This invention relates to an electroluminescent device and, more particularly, to an electroluminescent panel for emitting light through the electroluminescence and a lighting device using the electroluminescent panel.
A typical example of the electroluminescent panel is shown in FIG. 1 of the drawings. The prior art electroluminescent panel largely comprises a transparent package films 6 and light emitting body. The transparent package films 6 are laminated on each other, and are bonded to each other along the periphery 7 thereof (see FIG. 2). As a result, an inner space is defined between the transparent package films 6, and the light emitting body is provided in the inner space.
The light emitting body includes a non-transparent back electrode 1, a transparent electrode 2 and a fluorescent layer 3. The transparent electrode 2 is formed on the front surface of the fluorescent layer 3, and the back surface of the fluorescent layer 3 is covered with the non-transparent back electrode 1. The transparent electrode 2 is formed of indium tin oxide, and the back electrode 1 is formed of conventional conductive metal. When the transparent electrode 2 is biased with respect to the non-transparent back electrode 1, the fluorescent layer 3 emits light as indicated by arrow in FIG. 2.
The electric power is supplied through a pair of power supply lines 4 to the transparent/back electrodes 2/1. One of the power supply lines 4 is directly connected to the back electrode 1. The other of the power supply lines 4 is connected to a non-transparent power feeding layer 5, which is held in contact with the transparent electrode 2. The non-transparent power feeding layer 5 is formed of silver paste. The non-transparent power feeding layer 5 is patterned like capital letter xe2x80x9cIxe2x80x9d, and extends along a side line of the transparent electrode 2. The reason why the non-transparent power feeding layer 5 is required is that the silver paste is much smaller in resistivity than the indium tin oxide. If the power supply line 4 is directly connected to the transparent electrode 2, the potential level is decreased on the transparent electrode 2, and the light emitting body loses the brightness inversely proportional to the distance from the contact point between the power supply line 4 and the transparent electrode 2 as shown in FIG. 3. The non-transparent power feeding layer 5 makes the transparent electrode 2 equal in potential level along the side line, and the gradation is moderated (see FIG. 4). Thus, the non-transparent power feeding layer 5 is desirable for the light emitting body in so far as the highly-resistive non-transparent electrode 2 is used for the light emitting body. However, the non-transparent power feeding layer 5 makes the light emitting surface narrow. In other words, dark area takes place in the prior art electroluminescent panel from the inner edge of the non-transparent power feeding layer 5 to the outer edge of the transparent package film 6 as indicated by hatching lines in FIG. 1.
If the non-transparent power feeding layer 5 is patterned like capital letter xe2x80x9cLxe2x80x9d, i.e., extending along two end lines of the transparent electrode 2, the gradation is further moderated. However, the dark area is widened. Thus, there is a trade-off between the gradation of brightness and the dark area. Research and development efforts have been made for an electroluminescent panel free from the problems. A solution is disclosed in Japanese Utility Model Publication of Unexamined Application No. 5-55494. The prior art electroluminescent panel disclosed therein has a light emitting body wrapped in package films. The light emitting body includes a fluorescent layer sandwiched between a transparent electrode and a back electrode. A difference from the light emitting body shown in FIG. 2 is an elongated transparent electrode. Although the side line of the transparent electrode 2 is aligned with the side line of the fluorescent layer 3, the transparent electrode of the light emitting body extends over the side line of the fluorescent layer, and is folded down under the back electrode. A power supply lead is held in contact with the back electrode, and the back electrode and the power supply lead are covered with a water absorbing layer. The folded portion of the transparent electrode is held in contact with the water absorbing layer. A non-transparent conductive metallic layer is patterned on the folded portion of the transparent electrode, and a power supply lead is connected to the non-transparent conductive metallic layer. Thus, both of the transparent electrode and the back electrode are located on the same side with respect to the fluorescent layer, and any non-transparent layer is not formed on the transparent electrode over the fluorescent layer. When a bias voltage is applied between the transparent electrode and the back electrode, the light emitting body radiates light through the transparent electrode and the package film to the outside thereof. There is not any obstacle on the optical path from the light emitting body toward the outside. This results in that the dark area is narrowed.
However, a problem is encountered in the prior art electroluminescent panel disclosed in the Japanese Utility Model Publication of Unexamined Application in that the periphery of the package films is still dark. When the prior art electroluminescent panels are arrayed for forming a back light source for a panel display, plural prior art electroluminescent panels are contiguous to one another at the peripheral areas, and dark area takes place like a net.
It is therefore an important object of the present invention to provide an electroluminescent panel, the peripheral area of which is bright.
It is also an important object of the present invention to provide a lighting device implemented by an array of the electroluminescent panels.
To accomplish the object, the present invention proposes to sideward radiate light from a folded portion of a light emitting body.
In accordance with one aspect of the present invention, there is provided an electroluminescent panel comprising a package having an inner space, a light emitting body accommodated in the inner space and including a fluorescent layer for emitting light, a high-conductive non-transparent electrode formed on one major surface of the fluorescent layer and a low-conductive transparent electrode formed on the other major surface of the fluorescent layer, at least a part of the fluorescent layer and an associated part of the low-conductive transparent electrode being folded so as to overlap the aforesaid one major surface therewith, and a power supply system including a first power supply lead connected to the high-conductive non-transparent electrode, a high-conductive power feeding layer formed on the associated part of the low-conductive transparent electrode and a second power supply lead connected to the high-conductive power feeding layer.
In accordance with another aspect of the present invention, there is provided a lighting device comprising plural electroluminescent panels for providing light emitting surface, and each of the electroluminescent panels comprising a package having an inner space, a light emitting body accommodated in the inner space and including a fluorescent layer for emitting light, a high-conductive non-transparent electrode formed on one major surface of the fluorescent layer and a low-conductive transparent electrode formed on the other major surface of the fluorescent layer, at least a part of the fluorescent layer and an associated part of the low-conductive transparent electrode being folded so as to overlap the aforesaid one major surface therewith and a power supply system including a first power supply lead connected to the high-conductive non-transparent electrode, a high-conductive power feeding layer formed on the associated part of the low-conductive transparent electrode and a second power supply lead connected to the high-conductive power feeding layer.